1. Field of the Invention
The present invention relates to a printing plate made of rolled sheet metal and a process for producing printing plates from rectangular panels cut from a rolled sheet metal strip.
2. Description of the Related Art
Printing plates are rolled or placed on plate cylinders of printing machines. The edges at the circumferential ends of the printing plates are turned over and the turned over edges are received and clamped on the plate cylinders for holding the printing plate on the cylinder. One of the flat sides of the printing plate has a surface for receiving an image via printing technology. The surface which receives the image is grained, i.e., roughened or coated, and may also have a light-sensitive or laser sensitive covering.
The starting material for printing plates is a rolled sheet metal strip such as aluminum. The maximum width of a rolled sheet metal strip is limited by the capabilities of the rolling mills. Normal width printing plates may be cut from the sheet metal strips such that the circumferential edges of these normal width printing plates are transverse to the rolling direction of the strip. Accordingly, the turned over edges which are clamped are also transverse to the rolling direction. The sheet metal strip may already comprise a surface on which an image may be set. However, printing plates for extra-wide printing machines are wider than the width of rolled sheet metal strip. Therefore, when producing printing plates for extra wide machines, the extra-wide printing plates must be cut transverse with respect to the rolling direction because the width of these extra-wide printing plates exceeds the maximum strip width capabilities of rolling mills. A result of this configuration is that the turned over edges for extra wide printing plates are typically substantially parallel to the rolling direction of the sheet metal strip used to form the printing plate.
The crystal axes of rolled materials are aligned in the rolling plate and in the rolling direction. This alignment of the crystal axes produces an increased strength along the rolling direction. However, there is an increased tendency for tears to occur in the longitudinal direction. Because of this characteristic, extra wide printing plates are susceptible to fractures, especially at the turned over ends, after they have rolled over very few times during printing operations. Therefore, the service life of extra wide printing plates is significantly shorter than printing plates having a normal width.
The object of the invention is to provide an extra-wide printing plate having increased service life compared to the prior art and to provide a process for the production of the inventive extra-wide printing plates.
According to an embodiment of the present invention, the object is achieved by a printing plate in which a length and a width of the printing are arranged obliquely to the rolling direction of the sheet metal strip from which the printing plate is cut. As stated above, a rolled material has increased material strength along the rolling direction. Therefore, at least one component of the loading vector of the printing plate lies in the direction of increased material strength due to the oblique arrangement of the length and width. As a result, the service life of the printing plate is prolonged. Using the process according to the invention, it is possible to produce extra-wide printing plates with increased strength in the stress direction. Images of a number of pages can be set alongside one another on extra-wide printing plates. The resulting extra-wide printing plates are used on very wide printing machines, which process printing-material web widths of, for example, more than 1460 mm paper width.
Other objects and features of the present invention will become apparent from the following detailed description considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed solely for purposes of illustration and not as a definition of the limits of the invention, for which reference should be made to the appended claims. It should be further understood that the drawings are not necessarily drawn to scale and that, unless otherwise indicated, they are merely intended to conceptually illustrate the structures and procedures described herein.